1. Field of The Invention
The invention relates to an air conditioning system for airplanes for conditioning the moisture containing air, which is under excess pressure, for air conditioning an airplane cabin.
2. Prior Art
The fresh air for air conditioning airplane cabins is conditioned from the air, the socalled bleed air, which is bled from the power plant at high pressure and high temperature. The air conditioning systems use the pressure and temperature potential of the power plant air to generate the requisite cooling capacity. The bleed air is cooled in the course of the fresh air conditioning process, dehumidified and expanded to the cabin pressure of approximately 1 bar during ground operations or approximately 0.8 bar during flight operations. Air dehumidification is especially relevant during the fresh air conditioning process in order to prevent the individual components of the air conditioning system from icing up and in particular to prevent the formation of ice crystals and mist in the fresh air to be conditioned. Of course, it is necessary to dehumidify predominantly in the ground area, because during flight operation, that is at high altitudes, the ambient air and thus the bled power plant air is extremely dry in any event.
The German patent application DE 100 36 443.8, which has not been previously published, proposed an air conditioning system for airplanes for conditioning the moisture containing air, which is under excess pressure, for air conditioning an airplane cabin. The system comprises at least one compressor for compressing the air, fed under excess pressure, to an even higher pressure; a first air expansion turbine for expanding the air to a lower pressure; a second air expansion turbine, which is downstream of the first one, to further expand the air; and a water separator, which is disposed between the first air expansion turbine and the second air expansion turbine. With this air conditioning system, the air can be largely dehumidified. Of course, this air conditioning system, like other prior art air conditioning systems, does not provide a control mechanism for the moisture content of the air that is available for air conditioning the airplane cabin.
Therefore, the object of the present invention is to improve this class of air conditioning system in such a manner that it is possible to control at the same time the moisture of the air that is available for air conditioning the airplane cabin without suffering any losses in the cooling capacity.
The invention solves this problem through a combination of features by providing an air conditioning system for airplanes that removes moisture contained in the air, under excess pressure. The air conditioning system comprises at least one compressor for compressing the air, which is already fed under excess pressure, to an even higher pressure. There is also a first air expansion turbine for expanding the air to a lower pressure, and a second air expansion turbine, which is downstream of the first air expansion turbine, to further expand the air. Another feature is a water separator which is positioned between the first air expansion turbine and the second air expansion turbine. The water separator selectively adjusts the air expansion in the first air expansion turbine.
In the inventive air conditioning system the component that serves the purpose of dehumidification is installed after the first air expansion turbine. Thus, the highly compressed, but still moist air, coming out of the main heat exchanger, is passed to the first air expansion turbine at approximately 45 degrees C.
From the air expansion turbine, the air that is expanded in a first step, but is still moist and in which the moisture condenses in very fine droplets due to the temperature drop, is passed into the water separator, which can comprise, for example, a drop coalescing unit and a water separator, which follows the drop coalescing unit.
The present invention benefits from the fact that the degree of condensed droplets depends on the temperature level, to which the highly compressed, but still moist air, which is passed into the turbine, is decreased. The higher the degree of air expansion is, the lower the temperature level of the air. As the temperature level decreases, the percentage of free water that condenses increases.
By adjusting selectively the degree of air expansion, the residual moisture in the air can be adjusted. Hence, the combination of the features of the air conditioning system which comprises at least one compressor for compressing the air to an even higher pressure, the first air expansion turbine that expands the air to a lower pressure, and the second air expansion turbine, positioned downstream from the first air expansion turbine, further expands the air.
Also, the water separator positioned between the first and second air expansion turbine removes water from the air which makes it possible to control the moisture of the air provided to air condition the airplane cabin.
Especially advantageous embodiments of the invention include the first air expansion turbine exhibiting variable nozzle cross sections, with the nozzle cross sections preferably changed by a gate valve.
In another embodiment, the first air expansion turbine of the air conditioning system exhibits a twin nozzle, which is connected to separate air feeds, so that one of the feeds can be blocked to selectively choose a desired nozzle.
A further embodiment includes a bypass for the first air expansion turbine. The bypass permits at least one substream of the air to be directed past the first air expansion turbine. Also, the bypass can be activated to open or close a gate valve.
In another embodiment of the air conditioning system, a fraction of the air stream can be controllably and directly fed by a control valve from the inlet or outlet of the second compressor behind the first air expansion turbine.
A still further embodiment provides for a humidifier for the air, bled from a power plant, disposed upstream of the primary heat exchanger.
In a still further embodiment, in addition to the degree of air expansion in the first air expansion turbine and the degree of air expansion in the second air expansion turbine, the air conditioning system can be selectively adjusted in several ways. Additionally, the second air expansion turbine can have variable nozzle cross sections. The nozzle cross sections of the secondary expansion turbine can be changed by a gate valve. Alternatively, the second air expansion turbine can have twin nozzles which are connected to separate air feeds, and one of the feeds can be blocked in the second air expansion turbine. A bypass is provided that can direct a substream of the air past the air expansion turbine, and a gate valve is provided to open and close the bypass.
The air conditioning system, can also have a fraction of the air controllably fed by a control valve at the inlet or outlet of the compressor behind the first air expansion turbine.
In another embodiment, the first and second air expansion turbines are on a common shaft and the nozzle cross sections are coupled for adjustments. Alternatively, the first and second air expansion turbines are on separate shafts, and the nozzle cross sections of the first and second air expansion turbines are separately adjustable as a function of each other.
Preferably, the first air expansion turbine exhibits variable nozzle cross sections. By adjusting the nozzle cross sections, the degree of expansion that can be achieved in the air expansion turbine can be adjusted in a simple manner. The smaller the nozzle cross section is set, the higher the degree of expansion can be achieved with the air expansion turbine. The nozzle cross section can be varied by means of suitably actuated gate valves.
According to another, but more complicated alternative, the degree of expansion can also be changed by adjusting the guide vanes in the air expansion turbine.
According to a simple embodiment, the first air expansion turbine exhibits a twin nozzle, where each part of the twin nozzle exhibits a separate feed and where one of these feeds can be blocked.
According to another alternative embodiment, the first air expansion turbine is provided with a bypass which may be controlled so as to open or close by means of a gate valve. With the bypass, a part of the highly compressed air can be delivered directly into the water separator by bypassing the turbine. In the water separator, only a very small fraction of the free water can be extracted.
According to another improved embodiment, the second air expansion turbine can also exhibit variable nozzle cross sections. To the extent the air expansion turbines are disposed on different shafts, the nozzle cross sections are adjusted by choice independently of each other. However, in the case that the two turbines are disposed side by side on a shaft, a combined adjustment of the nozzle cross sections can be especially advantageous.
Another embodiment of the invention provides a connecting line between the outlet or inlet of the second compressor and the outlet of the first air expansion turbine. This connecting line exhibits a control valve, by means of which, depending on the need, at least one part of the air stream from the compressor can be delivered again directly behind the air expansion turbine. Thus, comparatively moist air can be generated by bypassing the first air expansion turbine; and optionally the turbine can be protected from icing up.
For targeted active humidification of the air provided for air conditioning the airplane cabin, a humidifier can be provided that immediately raises the bleed air to a desired moisture level before entry into the primary heat exchanger.
Thus, the moisture content in the air, provided for air conditioning the airplane cabin, can be adjusted over a wide range with the air conditioning system, according to the present invention.
These together with other objects and advantages which will become subsequently apparent reside in the details of construction and operation as more fully hereinafter described and claimed, reference being had to the accompanying drawings forming a part hereof, wherein like numerals refer to like parts throughout.
Other details and advantages of the invention are explained in detail with reference to the embodiments depicted in the drawings.